topic How to specify a datum transformation in .NET Maps SDK Questions

How to specify a datum transformation

MarkCederholm — Tue, 07 Oct 2014 16:06:44 GMT

If I want to project a point from WGS1984 (4326) to NAD1983 (4269) using transformation NAD_1983_To_WGS_1984_5 (1515), how do I go about doing it? Apparently I need to build a well-known text, but when I try the following it doesn't give the correct result:

			string sGEOGCS = "GEOGCS[...";
			string sGEOGTRAN = "GEOGTRAN[...";
			string sWKT = sGEOGCS + " " + sGEOGTRAN;

			MapPoint ptWGS84 = new MapPoint(dLon, dLat, new SpatialReference(4326));
			SpatialReference srTrans = new SpatialReference(sWKT);
			MapPoint ptNAD83 = (MapPoint)GeometryEngine.Project(ptWGS84, srTrans);

Re: How to specify a datum transformation

dotMorten_esri — Tue, 07 Oct 2014 18:18:41 GMT

Explicitly-defined datum transformations are not supported in the .NET SDK in this release. However simple datum transforms are already applied automatically when possible.

Re: How to specify a datum transformation

MarkCederholm — Tue, 07 Oct 2014 19:06:06 GMT

Thanks for your reply. While the geographic results are not exactly the same as those using ArcObjects, I projected them further to UTM and found that they're only a centimeter apart, which is good enough for my app.

Re: How to specify a datum transformation

AnnaLambrechtsen — Thu, 30 Oct 2014 00:21:33 GMT

i appreciate it's not in there currently, but i just want to confirm that it's needed.

in New Zealand there are some odd projections that are certainly not in the simple list you mention which require datum transformations to convert between.

at the moment i'll be using the REST API to do this conversion, but it'd be nice to not have to.

Re: How to specify a datum transformation

dotMorten_esri — Thu, 30 Oct 2014 02:30:34 GMT

Thanks Anna. We definitely have it on our future roadmap! There's also already a way to deploy extra datum grids that the projection engine will automatically use.